A polymer electrolyte fuel cell typically includes an anode and cathode electrode sandwiching a polymer membrane that selectively transports ions between the electrodes. The electrodes typically include a catalyst layer and a gas diffusion layer. The polymer membrane in combination with the anode and cathode electrodes is commonly refered to as a Membrane Electrode Assembly (MEA).
A general configuration of this fuel cell is shown in FIG. 1. As shown, a pair of catalyst layers 2 sandwich polymer electrolyte membrane 1. The electrodes are typically composed of a metal catalyst such as platinum supported by carbon and the polymer electrolyte membrane is used to selectively transport hydrogen ions from one catalyst layer to another. A polymer electrolyte membrane that can transport hydrogen ions is typically composed of a fluorinated polymer containing sulfonic acid groups. A pair of gas diffusion layers 3, which are gas permeable and conduct electricity, are positioned over the outer surfaces of catalyst layers 2. In this structure, electrode 4 is composed of gas diffusion layer 3 and catalyst layer 2. A gas diffusion layer is usually made up of a porous carbon based material, which includes carbon powder and fluorinated resin. Carbon paper, cloth sheet, felt, etc. are generally used as the support for the porous diffusion layer. Separator 6 is typically electrically conductive and mechanically fixes electrodes 4 on either face of polymer electrode membrane 1. Separator 6 additionally contains gas channels 7, which are located on its surfaces so that they face the electrodes and can be used to supply reaction gases to the electrodes and to remove excess gas and waste gas generated by the electrochemical reaction.
The gas channels are generally formed by creating a groove on the separator surfaces, although it is possible to detach them from the separators. A cooling water channel 8 can be created on the other surface of the separator to circulate water to maintain the cell's temperature. Gas is supplied to the gas channel on each separator from a manifold which can be internal or external to the separators. The outlet from the gas channel is also connected to a manifold which carries away the waste water and excess gas.
To prevent the fuel and oxidant that are supplied to the electrodes from leaking to the outside of the cell and from mixing with each other, gaskets 5 are provided around the edge of electrodes 4. A gasket is typically made of an O-ring, a rubber sheet, or a sheet composed of an elastic resin and rigid resin. The gas seals and gaskets are integrated with the electrodes and polymer membrane and are typically assembled in advance. At least one electrically conductive separator is placed between adjacent MEA's to electrically connect the MEA's in series with each other, and to provide mechanical support. In a fuel cell structure, MEA's, separators and cooling sections are aligned in alternating layers to form a stack of 10-200 cells, and the ends of the stack are sandwiched with current collector plates and electrical insulating plates and the entire unit is secured with a fastening rod.
Electrolyte membranes used for this type of fuel cells are very thin and are easily damaged, however. For example, they may be damaged by the cross section of the gasket. To address this potential damage, new shapes for the cross section of the gasket have been proposed. For example, Japanese Patent Application No. 2001-351651 discloses a variety of shapes for a gasket which contacts the electrode in the fuel cell as a means to address damage to the polymer electrolyte membrane. Japanese Patent Application No. 2002-329504 addresses the damage to an electrolyte membrane by inserting a frame-shaped seal between the membrane and an electrode.
The gas diffusion layer placed on a catalyst layer can easily damage the electrolyte membranes as well because the layers are often not cleanly cut when manufactured and therefore the edges of the layers may have pointed protruding carbon fibers as a result of such incomplete cuts. If the base of the layer is made of thin carbon paper, the edges of the layer would have numerous minute cracks, and these cracks are one of the main causes of damage to the electrolyte membrane. Once the electrolyte membrane is damaged, a direct short circuit and/or gas leak may occur at the damaged area. This aggravates damage to the fuel cell further.
Accordingly, a continuing need exists to provide a durable electrolyte membrane electrode assembly that is easily assembled without damage to the membrane.